Kelly Sears and her dog Theo are rarely apart. She takes him everywhere, but not just for companionship.
Sears has narcolepsy, a rare brain disorder that can cause her to fall asleep at any time without warning.
Theo is a specially trained "medical detection" dog that alerts her to changes in her body that might precede a narcolepsy episode.
"Before Theo, I didn't go out on my own ever. With Theo ... if I fall he'll immediately nudge and nudge and bark until I wake up," Sears said.
Many dogs like Theo are trained at a facility near London to smell chemical changes that might signal the presence of different diseases, such as bladder cancer.
"It's taken some time to get over the skepticism, but this is evidence-based work," said Claire Guest, chief executive of Medical Detection Dog.
Guest said it's medically proven that disease has odor and dogs are able to detect the smell. Some dogs even have a 93 percent accuracy rate.
"It's a new, non-invasive way of keeping people safe and of detecting human disease," Guest said.
Dogs like Theo also help change the perception of what it means to live with a disease like narcolepsy
"It would be nice for other people to see how well she's doing, to give them the encouragement as well," said Lynn Sears, Kelly Sears's mother.
Together, Theo and Kelly make a strong team.